The increasing number of communication standards and the centralization of all these standards within a single portable communication apparatus are difficult to achieve. Specifically, in order to transmit and receive on each of the bands concerned by these standards an oscillating element capable of operating continuously on all these frequency bands must be used. An oscillating element comprising a juxtaposition of several oscillating circuits does not allow a continuous operation between the frequency bands. Another oscillating element comprising a single oscillator with a tunable frequency does not allow a sufficient amplitude of frequency variation.
A chosen solution usually consists of using a single circuit supplying several oscillators, making operation possible on several bands. The use of a single circuit also makes it possible to reduce costs and make miniaturization of the electronic circuit easier.
In this type of circuit, the induction coils of each of the oscillators may also be mutually coupled electromagnetically. Therefore, in patents U.S. Pat. No. 7,423,495 and WO 2006/020873, several oscillating circuits are mutually coupled via induction coils. The values of the induction coils vary depending on the modes of the other oscillators and this makes it possible to multiply the number of operating modes.